1. Field of the Invention
The invention relates generally to exhaust gas recirculation controls for internal combustion engines and particularly relates to such a control wherein the amount of exhaust gas recirculated is varied as a function of engine load and speed.
2. Description of the Prior Art
Control devices are known which provide for the recirculation of exhaust gases through an internal combustion engine to control the emission of oxides of nitrogen. Most have recirculated a fixed percentage of exhaust gases as a function of engine speed and are configured to provide the optimum amount of exhaust gas recirculation during the high load, hard acceleration mode of operation of the engine. They consequently permit more recirculation than is desirable during lightly loaded, higher speed operation. This adversely affects engine performance in terms of reducing the emission of oxides of nitrogen.
Another disadvantage noted in the prior art devices results from their being constructed to effect the control of exhaust gas flow from the engine exhaust manifold to the engine inlet manifold in response to changes in pressure differential between the pressure of the exhaust gases across a fixed control orifice in the exhaust stream. This results in a wide range of pressure differential within normal exhaust system tolerances.